May 18, 2013

May 18, 2013: Target Areas Range from sw Nebraska to scentral KS

Significant Risk for Tornadic Supercells over Broad Area Today

Thom and I are just heading south from North Platte.   

While significant CAPE exists from I80 south surmounted by more than adequate storm relative shear for supercells, I don't much like the storm motions relative to the dry line and the mid tropospheric winds further north for sustained discrete convection and storms that don't collide with other storms' cold outflows.

The RAP and WRF-NAM are really confused about progged dew point and CAPE/CIN fields.   But both are in agreement about the strong surface pressure falls in sw KS with the low pressure area developing eastward into that area  and a dry line bulge coming out of OK into that area.   The forecast hodographs are impressive for the area from Wichita west to Dodge CIty and up to I70.   So right now we are targeting that area.

However, we are going to think harder about that target when we get to McCook or so.  The HRRR is consistent too in showing cells in SW Nebraska with a lot of updraft helicity.  But later runs also show really imprssive looking cells in south-central KS.

Below I've included the WRF-NAM forecast for Pratt KS at around 7PM this evening.  The buoyancy is really upper end, with 5000 J/kg and no CIN.  Metr 201 and 698 students will remember that the forecast for maximum upward velocity (assuming no entrainment and no turbulent mixing) is the square root of 2 X CAPE.  In reality, maximum updraft at the EL will be about 1/3 or lsss of that....but that's till nearly 100 mph....enough to justify the forecast of cantaloupe sized hail.